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musculoskeletal system 3 > 8. peripheral nerve injuries > Flashcards

8. peripheral nerve injuries Flashcards

1
Q

What 2 units make up peripheral nerves?

A

motor unit

  • anterior horn cell (located in grey matter of spinal cord)
  • motor axon
  • innervates muscle fibres (neuromuscular junctions)

sensory unit

  • cell bodies in posterior root ganglion
  • ie lie outside spinal cord
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2
Q

Where is the cell body for the motor unit of peripheral nerves?

A
  • Anterior horn cell (located in grey matter of spinal cord)
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3
Q

Where is the cell body for sensory unit of peripheral nerves?

A
  • Cell bodies in posterior root ganglion, so lie outside spinal cord
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4
Q

Explain the ventral and dorsal roots eventually forming peripheral nerves?

A

nerve fibres joint to form ventral motor roots and dorsal sensory roots, these combined to form spinal nerve

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5
Q

What do spinal nerves exits the vertebral column through?

A

Intervertebral foramen

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6
Q

Describe the structure of peripheral nerves from deep to superficial?

A

Axons coated with endoneurium, grouped into fascaicles (nerve bundles), covered with perineuriu, grouped to form nerve covered with epineurium

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7
Q

What does nerve fibre diameters range between?

A

0.3-22um

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8
Q

What forms a thin cytoplasmic tube around nerve fibres of peripheral nerves?

A

Schwann cells

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9
Q

What are the different fibre types from smallest to largest?

A
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10
Q

What is the speed of each fibre type?

A
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11
Q

What is the function of each fibre type?

A
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12
Q

How does diameter of a fibre impact speed of transmission?

A

With increasing diameter comes increasing speed of transmission

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13
Q

What are the different categories of injuries to peripheral nerves?

A

Compression

Trauma

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14
Q

When does compression of peripheral nerve occur?

A

Due to nerve palsies or entrapement

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15
Q

What are some examples of nerve compression due to entrapment?

A
  • Carpal tunnel syndrome
    • Median nerve at wrist
  • Sciatica
    • Spinal root by intervertebral disc
  • Morton’s neurom
    • Digital nerve in 2nd or 3rd webspace of forefoot
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16
Q

What are the 3 categories of trauma injuries to peripheral nerves?

A
  • neurapraxia
  • axonotmesis
  • neurotmesis
17
Q

Describe neurapraxia?

A
  • nerve in continuity
  • stretched or bruised
  • reversible conduction block due to local ischaemia and demyelination
  • prognosis good
18
Q

Describe axonotmesis?

A
  • endoneurium intact but disruption of axons (more severe than neurapraxia)
  • stretched or crushed or direct blow
  • wallerian degeneration follows
  • prognosis is fair
19
Q

What kind of degeneration follows axonotmesis?

A
  • Wallerian degeneration follows so nerve fibre effectively disappears
20
Q

Describe neurotmesis?

A
  • complete nerve division
  • laceration or avulsion
  • no recovery unless repaired by direct suturing or grafting
  • endoneural tubes disrupted so high chance of ‘miswiring’ during regeneration, leading to large neuroma
  • prognosis poor
21
Q

What is used to grade trauma to peripheral nerve?

A

Sunderland grading

22
Q

Describe the sunderland grading system?

A
23
Q

Nerve injuries can be described as open or closed, which of neuropraxis, axonotmesis and neurotmetic is each?

A

Closed - neuropraxis, axonotmesis

Open - neurotmesis

24
Q

Which of closed and open nerve injuries heals better?

A

Closed injuries - spontaneous recovery possible (better)

Open injuries - treated with early surgery

25
Q

What are closed nerve injuries typically caused by?

A
  • Typically stretching of the nerve
    • Brachial plexus injuries
    • Radial nerve injuries due to humeral fractures
26
Q

What part of nerve undergoes Wallerian degeneration in open nerve injuries?

A
  • Distal portion of nerve undergoes Wallerian degeneration
27
Q

What are the clinical features of peripheral nerve injuries?

A
  • Dysaethesiae (disordered sensation)
    • Anaesthetic (numb), hypo and hyper-aesthetic paraesthetic (pins and needles)
  • Motor
    • Paresis (weakness) or paralysis with or without wasting
    • Dry skin
  • Reflexes
    • Diminished or absent
28
Q

What is the medical term for disordered sensation?

A

Dysaesthesia

29
Q

What is the medical term for pins and needles?

A

Paraesthesis

30
Q

What is the medical term for weakness?

A

Paresis

31
Q

Describe the healing of peripheral nerves?

A
  • Slow
  • Starts with initial death of axons distal to site of injury
    • Wallerian degeneration
    • Then degradation of myelin sheath
  • Proximal axonal budding (start of growth) occurs after 4 days
    • Rate of growth 1-3mm/day
  • Tinel’s sign can monitor recovery
    • Tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed
    • Also by electrophysiological nerve conduction studies
32
Q

What is the rate of new axonal growth?

A

1-3mm/day

33
Q

How can growth of new nerves after injury be monitored?

A
  • Tinel’s sign can monitor recovery
    • Tap over site of nerve and paraesthesia will be felt as far distally as regeneration has progressed
    • Also by electrophysiological nerve conduction studies
34
Q

What does prognosis of peripheral nerve injuries depend on?

A
  • Whether pure nerve (only sensory or motor) or mixed nerve (both sensory and motor in same nerve)
  • How distal the lesion is (proximal is worse)
35
Q

What are some nerve repair methods?

A
  • Direct repair
    • Can happen due to laceration if no loss nerve tissue
    • Microscope/loupes
    • Bundle repair
    • Growth factors
  • Nerve grafting
    • If nerve loss has occurred
    • Late repair
      • Use sural nerve to provide tubes to connect nerve endings
36
Q

Compare and contrast UMN and LMN in terms of:

  • strength
  • tone
  • deep tendon reflexes
  • clonus
  • Babinski’s sign
    atrophy
A

musculoskeletal system 3 (46 decks)

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